You're in the middle of what appears to be a routine cataract surgery. A round 5-mm diameter capsulorrhexis was created, and no zonular weakness was detected. The nucleus was removed with phaco and the cortex fully aspirated. The capsular bag has been inflated with viscoelastic, and you're now ready for IOL insertion. The IOL is the Hoya iSert pre-loaded IOL, so you know that the IOL was properly positioned in the injector.

Why is the IOL decentered? And what is your next move?

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See Dr. Devgan share more expert insight live at OSN New York 2010, to be held November 19-21, 2010 at the Sheraton New York Hotel & Towers. Learn more at OSNNY.com.

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When a patient has a small pupil due to rubeosis iridis from neovascular disease, how do you handle it during cataract surgery?

Neovascularization and scarring of the iris in a patient with proliferative diabetic retinopathy.

In the case presented here, a 60-year-old patient had a history of proliferative diabetic retinopathy including rubeosis iridis and neovascularization of the angle. She responded well to panretinal photocoagulation laser as well as intravitreal injections of anti-VEGF medications. The neovascularization had regressed, leaving a scarred iris and a tonic pupil of approximately 4 mm in diameter. She now required cataract surgery.

In most cases, small pupils can be stretched to allow expansion to a size sufficient for routine cataract surgery. But in this case, there was a risk that stretching the pupil may rupture some of the rubeotic vessels of the iris. While these vessels were mostly regressed and fibrosed, there was a risk of vascular rupture and bleeding.

And to top it off, the patient was already on warfarin as a blood thinner because of her atrial fibrillation.

I found that the solution was for me to work through the small pupil and not stretch it. The patient's 4-mm pupil was sufficient to perform a 5-mm capsulorrhexis, and then the nucleus was chopped using a vertical chop technique. This technique allowed for placement of the phaco probe and the chopper within the central 4 mm of the nucleus so that everything was visible. Using a horizontal chop technique would have required placing the chopper around the nucleus periphery, which was not visualized.

With the nucleus chopped into quadrants, it was removed and then the cortex was aspirated. A three-piece acrylic lens with a 6-mm optic was placed in the capsular bag and rotated to help free any residual cortex. At the end, the chopper was used to lift up and peek under the iris to ensure complete cataract removal. The patient did well and is now following up with her retinal specialist.

See Dr. Devgan share more expert insight live at OSN New York 2010, to be held November 19-21, 2010 at the Sheraton New York Hotel & Towers. Learn more at OSNNY.com.

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In the last blog entry, I showed a case in which I performed an iris repair and IOL exchange. A reader asked why I removed the old IOL instead of simply repositioning it. That's a great question.

The old IOL was clearly decentered, and from the patient's chart, it was noted to be a lens with negative spherical aberration. This type of lens requires excellent centration with the patient's visual axis in order to properly offset the positive spherical aberration of the cornea. If I could be sure that the original IOL was in good condition and without damage, then I could re-center the lens in the visual axis. This would not be an easy task in this eye because the reconstructed pupil would shift to some degree due to the iris sutures. Additionally, at the beginning of the surgery, a chopper was used to lift the nasal iris, and it was noted that the nasal haptic of the lens was bent. The old IOL was removed, and it was replaced with an IOL with zero spherical aberration, which is relatively immune to decentration.

Negative spherical aberration IOLs work best when they are centered with the visual axis. Click image for larger view

In the diagram shown here, a negative spherical aberration IOL has a different power in the center than in the periphery — the opposite of the cornea. When the negative spherical aberration IOL is aligned with the cornea, the total spherical aberration of the eye is cancelled out and the patient achieves excellent visual quality. But when the negative spherical aberration IOL is decentered with respect to the visual axis, it does not evenly address the corneal positive spherical aberration and, as such, it induces coma. Coma is where the power is higher on one side vs. the other, and the result is a comet-shaped aberration of the image.

In routine cases, aspheric IOLs with negative spherical aberration are good choices because they tend to improve image quality. However, in eyes in which you think that there is a chance for IOL decentration, you may be better off using a zero spherical aberration IOL instead.

See Dr. Devgan share more expert insight live at OSN New York 2010, to be held November 19-21, 2010 at the Sheraton New York Hotel & Towers. Learn more at OSNNY.com.

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